1. Field of the Invention
The invention relates generally to polymer compositions with very low levels of residual contamination, and more specifically to compositions comprising a monoamine-endcapped polyimide component with very low levels of residual contamination.
2. Description of the Related Art
Polyetherimides are a class of polymers that display excellent high temperature performance and can be processed to make molded articles, fibers, films, foams etc. For example, polyimide resins such as ULTEM® resin grades 1000 or 1010 with a melt viscosity (MI) range of 0.8-1.1 and 1.6-2.0, respectively, find wide use in applications where high temperature performance and easy processability is required. However, these resins do not meet stringent cleanliness requirements that are dictated by newer, high end applications. High end applications of polyetherimides, such as in semiconductors or fibers, require the resin to have very low contamination levels, or the processability and/or product performance is adversely affected.
Common resin contaminants could be organic or inorganic in nature, The organic contaminants are mostly lower molecular weight species. One such low molecular weight species is phthalic anhydride m-phenylene diamine imide (PAMI), formed by the reaction of two moles of phthalic anhydride which is used as an end cap in the polymer reaction, and one mole of m-phenylene diamine (mPD), which is one of the monomers. This molecule has been found to ‘plate out’ on equipment parts during the molding operation. U.S. Pat. No. 6,919,422, which is hereby incorporated by reference in its entirety, provides details of a polyimide composition that solves the above plate out issue by replacing the PAMI end cap with a monoamine end cap, such as aniline. Thus, in the place of PAMI, a larger molecule is formed on the reaction of 2 moles of aniline with one mole of the dianhydride monomer. This molecule does not plate out to the extent that PAMI does. A common inorganic contaminant is stabilizer Irgafos 168 and its oxidized version. The stabilizer is added to the polymer prior to extrusion to lower color of the final resin. There is residual stabilizer in measurable quantity in the resin pellets post extrusion. The residual stabilizer is linked to higher particle counts in the resin.